(1) Field of the Invention
The present invention relates to a system and method for automatically changing a running characteristic of a vehicle, having an automatic transmission, according to a driving characteristic of a vehicle driver or according to a running environment.
(2) Background Art
To change a running characteristic (mode) of a vehicle, various types of systems have been proposed in which, e.g., several kinds of shift patterns for an automatic transmission are set and one of the shift patterns is selected according to a running condition and so on so that a gear speed range of the automatic transmission is shifted in accordance with respective optimum shift patterns for a street run, freeway run, or ascending/decending slope run.
A Japanese Patent Application First Publication (Unexamined) No. Showa 63-28741, published on Feb. 6, 1988, exemplifies a previously proposed system for controlling a gear shift range of an automatic transmission.
In the previously proposed gear shift range controlling system, an acceleration of the vehicle is derived from a differential value of a vehicle speed, and an absolute value of the acceleration is integrated to determine whether the vehicle is running on a street or on an ascending slope.
A Japanese Patent Application First Publication (Unexamined) Showa 62-180153, published on Aug. 7, 1987, exemplifies a previously proposed method for determining whether the vehicle having the automatic transmission is running on an ascending slope.
In the previously proposed method, the vehicle is determined to be running on an ascending slope when the vehicle speed is reduced and the gear speed range is shifted from a higher gear range to a lower gear range although engine output torque is maintained above a constant value.
Then, when the previously proposed method determines that the running condition is transferred to a particular state different from the previous shift pattern, a change in the shift pattern is immediately executed to change the running mode.
However, since the vehicle driver usually does not perceive that the running mode has been changed, vechicular behavior which reverses an expectation of the driver may occur as he or she may operate the vehicle assuming that the running mode is the same as before the change of shift pattern. Therefore, the driver may experience an unpleasant feeling while driving.
In addition, even if the driver predicts the change of shift pattern, the same unpleasant feeling is experienced for a duration of time during which the driver becomes accustomed to the new pattern. Since the feeling is different for each driver, this is a perplexing problem in drive operation which impairs enjoyment of the driving experience.
In addition to the case of shift pattern changing, the above applies equally well to corresponding relationships of an opening angle of an engine throttle valve with respect to a depression angle of an accelerator and of a mixture ratio of air fuel mixture with respect to the depression angle of the accelerator and to a case where a characteristic of the generated output of the engine such as ignition timing is changed according to running conditions.